Mineral N Distribution and Accumulation in Apple Orchards of Weibei Areas in Shaanxi Province

The NH~+_4-N and NO~-_3-N contents were determined in different soil depth profiles from 87 apple orchards in 8 counties in Weibei area of Shaanxi Province.The results showed that the content of ammonium nitrogen were 4.67±1.37 mg·kg~(-1) and didn't change much in 0~120 cm soil depth profiles of orchards in different apple producing regions,the content of nitrate nitrogen were 22.86±24.98 mg·kg~(-1) and changed largely from 0.33 to 119.8 mg·kg~(-1),the amount of NO~-_3-N had the tendency of becoming large with the depth of the soil layer,accumulating peak was mostly on 40~60 cm soil layer,then the accumulating amount was decreasing gradually.Orchard soils tested accumulated a large amount of nitrate nitrogen in 0~120 cm due to over-fertilization.